Yao Liu
18 August 2014
Ecological theory: To codify what we know (or what we believe we know, or what we want to explore), be explicit with our assumptions and logic. Formalizing the knowledge, put it to the test, and experiment with it.
Prediction and forecasting to support decision-making: e.g. forest responses to global change
Modeling is an interative process:
States and state variables
Inputs (parameters, meteorological and envrionmental drivers, surface conditions, etc.)
Outputs or predictions
Dietze and Latimer 2012
Terrestial biosphere models/ Ecosystem models: computer models used to predict the states and dynamics of terrestial ecosystems
What processes should we include in our models?
Enzyme Kinetic (Farquhar model)
\[ A = f(PAR,CO2,RH) \]
Long and Bernacchi, 2003
Light use efficiency (LUE)
\[ A = LUE*PAR*M(env) \]
To calculate GPP
\[ GPP = A * LAI \]
Modified by:
Recall that \[ NPP = GPP - Ra \] With BGC model \[ NEP = NPP - Rh \]
TECO model components:
Plant ecophysiology
Soil biogeochemistry
Flux = g * DX
T = Temperature
a = absorptivity
e = emissivity
L = latent heat of vaporization
C = heat capacity
z = solar zenith angle
Diagram by Dennis Baldocchi
Table 1 in Dietze and Latimer (2012) Forest Simulators. In Encyclopedia of Theoretical Ecology. University of California Press.
Parameter values you need to know before you could make predictions using a model like this?
Diagram by Dennis Baldocchi
Miller et al. (2008) Exploring climatic and biotic controls on Holocene vegetation change in Fennoscandia. Journal of Ecology
Lehsten, Doerte, et al. (2014) “Modelling the Holocene migrational dynamics of Fagus sylvatica L. and Picea abies (L.) H. Karst.” Global Ecology and Biogeography.
Wu et al. (2009) New coupled model used inversely for reconstructing past terrestrial carbon storage from pollen data: validation of model using modern data. Global Change Biology, 15, 82-96 .
Garreta et al., 2009
“[L]ike many areas of climate change science, but unlike most areas of ecology, the understanding of biosphere-atmosphere interactions fundamentally relies on the predictions of large, complex models whose parameters are difficult to measure, and that make predictions at scales far larger than we are typically able to make measurements. As a result, the findings of terrestrial biosphere modeling studies are usually appropriately couched in terms of ‘potential feedback mechanisms’. Indeed, a harsh, but not entirely unwarranted, view would be that our current understanding of biosphere-atmosphere feedbacks is a collection of interesting, but largely untested, hypotheses for the future state of terrestrial ecosystems and climate.” .
Moorcroft et al.(2006)
How well do current models simulate decadal-to-centennial ecosystem dynamics when confronted with past climate change, and what factors most limit model accuracy?
Activities:
1. Pre-settlement “potential vegetation” for the region based on running their model to equilibrium
2. New runs over the PalEON time period under common drivers from a small ensemble of different GCM
3. Compare models at points and to stats group's gridded data product
How sensitive are ecosystem models to initialization state and equilibrium assumptions? Do data-constrained simulations of centennial-scale forest dynamics improve 20th-century simulations? How long does initial condition matter?
What net carbon fluxes are compatible with an observed species composition and disturbance regime? Was the terrestrial biosphere a carbon sink or source during the Little Ice Age and Medieval Climate Anomaly?
With PalEON data products in hand, use data-assimilation to alter the model's state variables and disturbance regime in order to stay “on track” with the observations and take into account the uncertainties in those observations.
State-variable Data Assimilation:
To what extent does site-level data-model fusion improve regional model projections? Which parameters are most responsible for data-model divergences at decadal to centennial timescales, and how can they be improved? Where can we get most value from future field campaigns?